From nobody Mon Jun 8 22:55:25 2026 Received: from mail-pj1-f47.google.com (mail-pj1-f47.google.com [209.85.216.47]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 298F438AC9C for ; Tue, 26 May 2026 03:44:46 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.216.47 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779767088; cv=none; b=FjZS35eQhcJLigMqkmJTXOQT0tO1eTMqUGxOnloQ0bsjEaQ4NUZOKkn4EZc5JV4/E1mf/kP4qasnqJZeU+hxiitr2Xpb8N4g3Kc9l39rbWK0M/sa1qTAoaSO0DZBlo7Mb8nLaDHH1A+6okSZJYaJcI+YRdQi6ffZuDOM3UjAHyo= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779767088; c=relaxed/simple; bh=iXrjFvB8tMCVBctUR+4Zu2wfyYQdjZDR/MkrRJMim+0=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=ZO6tBs+SrIQPwqC/yLqt2eYMGJQirUpsI6wkRKo1xogiHIC2TUWij6mV5ai+p5VCf7gfI1IeyY1ku4qifrPDq4vzadE412bg+mObvREJXXQSVW4LjzxYyMd/7SsKK2yhlAf7Ze6hYorDQjQPCqT3Dm2dVJW217ZkGXZuR5lGIfs= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com; spf=pass smtp.mailfrom=gmail.com; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b=EpggUdVv; arc=none smtp.client-ip=209.85.216.47 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=gmail.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="EpggUdVv" Received: by mail-pj1-f47.google.com with SMTP id 98e67ed59e1d1-36a35e4eefeso3378716a91.1 for ; Mon, 25 May 2026 20:44:46 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20251104; t=1779767086; x=1780371886; darn=vger.kernel.org; h=content-transfer-encoding:mime-version:message-id:date:subject:cc :to:from:from:to:cc:subject:date:message-id:reply-to; bh=mIBdIvyjghcA5U0E+cK/NlWb2TAS2dmtADXjkP6n9ws=; b=EpggUdVvmOkkP96C/g1phEfJYsQcRd3xbop2hKNSSUcutGdZCHeVZPKl+LkMLSztzD tqg/Fiw8jC4La+IHszaXTqm/k7qLFBhTnnfRMt0n+Wv+h6vUk5+3lL9sDG/GQUx47svV rw4vSESMadCrvDStw5G3awD2JlPcCU+yIS1dZ/pMXo4FbrfvZlKcyObv+ItqYGFolajB NMCHfFuznL+gyO5uIrryeZAI5NwEJ2HvLbtQYfeq7IKUJat+1ueCLnTJEaySgOPmRuNR kktfY+k+h4kY9aiUJuFMzv8imeWZdL75QCt5WVM+tKRquqxy/XEZFdkoEndyjlXEOnPV 6sgA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1779767086; x=1780371886; h=content-transfer-encoding:mime-version:message-id:date:subject:cc :to:from:x-gm-gg:x-gm-message-state:from:to:cc:subject:date :message-id:reply-to; bh=mIBdIvyjghcA5U0E+cK/NlWb2TAS2dmtADXjkP6n9ws=; b=CiBtzk9x7Nf367tTTv37awU/7m2sYuffs8MZ2NygO00zR1URtTrXv4Y+BD43unxlao r6t+W84w840vz3OxfQ7M7iWs0B7RN+G7FZrakGtxof4izrTHOgzWiTYWGDiSdZ5/SAoJ LH09Zp8zaMhhLUFk64NwHewk9QgyJY73ERvFuqYBisywwAMOfZTdeX+uzpJRVzXe8G/b 6FcDT3i+503T/5Q6rdkZZUQNnqkcBvRFUfH3jTEkgy6aUwZiahOY8GiKZdBsTeflyN45 545FPB1TYhAIY7Qid3gcpZjravmxqSY+KsspVwFGArdyUJbHYBs5cOQi3bcRmJ4zP6l3 oUhg== X-Forwarded-Encrypted: i=1; AFNElJ+Ngj4d4IrRecbd4UCsz/LbF116hHaCM5utSV7SflAbPx/vmJCl0Lfqzd81+ZT498T+Z8E6qa01zQ3AhAU=@vger.kernel.org X-Gm-Message-State: AOJu0YxcHp15DGVnE8Kzix7YVSedw/Xy1eIjj3GagAr95cw3EqSX7XZF bMehDj2dLzy3n1hfoXvTATGN5jM3/Aqb+0TCib6b/8emO/Ql+LOOIo52 X-Gm-Gg: Acq92OFFHB+FiduYJ+k+Ciacj6M4qlXY9Bu5HabnMzTVjBuu3S0YV+y8vcmKUFldk7y iFHWdCq4YxbwxV5YM+mSnHHx7wpPYvln8oKuCACnrqjLVzQBm05DsXHGglQv6NeKgBxE9s3Rd2e yDgVN/vZqKhwwwy7ToS7yL+nVU8p2IgmzJWndV3kc3Kr1Q4WMVLG/NNpNJhMyq8VAIhM7DdGynq BUDPl0R7FCFKN9hTD/C9u7dupaDqiGFeJG4BT3gymEfZ44PV9fWn6GY8UNYC628yy74l727D78d LJ3TMt3eAdwZe9PEVTRgkasBgGQSIBuXWS/Yea1QS8XWPItcxu2OUWaieYEnfI7q0FRkngYb3TC 001ZJlNItdL77nS7NR1Ded3M78sIWY2XjBSQqWQVksXK2uip0LKY7Edzcuk5tuM6YndEalyT7L+ ZGGuYZzEw/6riCkmbldoCc0N3AbZxbc1X/d5Uyml6M0Qo3bIR39xoKdR+x2DGVWNARnkT2hg== X-Received: by 2002:a17:90b:5208:b0:35d:a5cb:95c1 with SMTP id 98e67ed59e1d1-36a676287b9mr16258291a91.23.1779767086338; Mon, 25 May 2026 20:44:46 -0700 (PDT) Received: from qiwenjie-ThinkCentre-M760t.mioffice.cn ([43.224.245.241]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-36a676e195asm5790623a91.1.2026.05.25.20.44.43 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 25 May 2026 20:44:45 -0700 (PDT) From: Wenjie Qi X-Google-Original-From: Wenjie Qi To: jaegeuk@kernel.org, chao@kernel.org Cc: linux-f2fs-devel@lists.sourceforge.net, linux-kernel@vger.kernel.org, qiwenjie@xiaomi.com, qwjhust@gmail.com, stable@kernel.org Subject: [PATCH v2] f2fs: avoid cp_wait use-after-free in f2fs_write_end_io() Date: Tue, 26 May 2026 11:44:39 +0800 Message-ID: <20260526034439.1017521-1-qiwenjie@xiaomi.com> X-Mailer: git-send-email 2.43.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" f2fs_write_end_io() decrements the writeback page counter before waking sbi->cp_wait for the last F2FS_WB_CP_DATA completion. That decrement can drop the F2FS_WB_CP_DATA count to zero. It can unblock a concurrent unmount path waiting in f2fs_wait_on_all_pages(). Unmount can then continue through f2fs_put_super() and free sbi while the end_io callback is still about to evaluate wq_has_sleeper() and wake_up() on sbi->cp_wait. Commit 2d9c4a4ed4ee ("f2fs: fix UAF caused by decrementing sbi->nr_pages[] in f2fs_write_end_io()") fixed one post-decrement sbi access by moving the warm-node-list handling before dec_page_count(). The compressed writeback path follows the same rule and documents that sbi accesses must happen before dec_page_count() can drop the F2FS_WB_CP_DATA count to zero. Use atomic_dec_and_lock_irqsave() for F2FS_WB_CP_DATA completions so the zero transition is serialized with cp_wait.lock. When the count reaches zero, wake waiters while holding the same lock. In f2fs_wait_on_all_pages(), prepare the waiter and recheck the page count while holding cp_wait.lock before sleeping. This keeps the wakeup visible to waiters without requiring the end_io callback to access sbi after the F2FS_WB_CP_DATA count has reached zero. It also avoids a missed wakeup that would otherwise make the waiter sleep until DEFAULT_SCHEDULE_TIMEOUT. Fixes: ce2739e482bc ("f2fs: fix to avoid UAF in f2fs_write_end_io()") Cc: stable@kernel.org Signed-off-by: Wenjie Qi --- fs/f2fs/checkpoint.c | 20 ++++++++++++++++++-- fs/f2fs/data.c | 25 +++++++++++++++++-------- 2 files changed, 35 insertions(+), 10 deletions(-) diff --git a/fs/f2fs/checkpoint.c b/fs/f2fs/checkpoint.c index c00a6b6ebcbd..b16d2d30ec6a 100644 --- a/fs/f2fs/checkpoint.c +++ b/fs/f2fs/checkpoint.c @@ -1497,24 +1497,40 @@ static void unblock_operations(struct f2fs_sb_info = *sbi) f2fs_unlock_all(sbi); } =20 +static bool f2fs_prepare_cp_wait(struct f2fs_sb_info *sbi, + struct wait_queue_entry *wait, int type) +{ + unsigned long flags; + bool wait_more; + + prepare_to_wait(&sbi->cp_wait, wait, TASK_UNINTERRUPTIBLE); + spin_lock_irqsave(&sbi->cp_wait.lock, flags); + wait_more =3D get_pages(sbi, type); + spin_unlock_irqrestore(&sbi->cp_wait.lock, flags); + + return wait_more; +} + void f2fs_wait_on_all_pages(struct f2fs_sb_info *sbi, int type) { DEFINE_WAIT(wait); =20 for (;;) { - if (!get_pages(sbi, type)) + if (!f2fs_prepare_cp_wait(sbi, &wait, type)) break; =20 if (unlikely(f2fs_cp_error(sbi) && !is_sbi_flag_set(sbi, SBI_IS_CLOSE))) break; + finish_wait(&sbi->cp_wait, &wait); =20 if (type =3D=3D F2FS_DIRTY_META) f2fs_sync_meta_pages(sbi, LONG_MAX, FS_CP_META_IO); else if (type =3D=3D F2FS_WB_CP_DATA) f2fs_submit_merged_write(sbi, DATA); =20 - prepare_to_wait(&sbi->cp_wait, &wait, TASK_UNINTERRUPTIBLE); + if (!f2fs_prepare_cp_wait(sbi, &wait, type)) + break; io_schedule_timeout(DEFAULT_SCHEDULE_TIMEOUT); } finish_wait(&sbi->cp_wait, &wait); diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c index d83a21998ec2..d92f0b70ba2f 100644 --- a/fs/f2fs/data.c +++ b/fs/f2fs/data.c @@ -392,15 +392,24 @@ static void f2fs_write_end_io(struct bio *bio) if (f2fs_in_warm_node_list(folio)) f2fs_del_fsync_node_entry(sbi, folio); =20 - dec_page_count(sbi, type); + if (type =3D=3D F2FS_WB_CP_DATA) { + unsigned long flags; =20 - /* - * we should access sbi before folio_end_writeback() to - * avoid racing w/ kill_f2fs_super() - */ - if (type =3D=3D F2FS_WB_CP_DATA && !get_pages(sbi, type) && - wq_has_sleeper(&sbi->cp_wait)) - wake_up(&sbi->cp_wait); + /* + * Hold cp_wait.lock across the zero transition and the + * wakeup so f2fs_wait_on_all_pages() cannot miss it or + * free sbi before this callback stops touching cp_wait. + */ + if (atomic_dec_and_lock_irqsave(&sbi->nr_pages[type], + &sbi->cp_wait.lock, + flags)) { + wake_up_locked(&sbi->cp_wait); + spin_unlock_irqrestore(&sbi->cp_wait.lock, + flags); + } + } else { + dec_page_count(sbi, type); + } =20 folio_clear_f2fs_gcing(folio); folio_end_writeback(folio); --=20 2.43.0